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  1. #1
    Join Date
    Jan 2005
    Location
    O.B.X
    Posts
    249

    Any Way To Calculate Target Subcool?

    I realize there is a calculation for your target superheat (eg. (IWB)*3-80-(OAT)/2=Target Superheat. However most units that I have come accross DO NOT specify the target subcooling (I speak of TXV/13 SEER units of course). I was wondering if anybody here knew of some calculation to determine this. I realize that 10 degrees will never get you in trouble, but I have read that fixed orifices can require much higher subcool levels. I Maybe chasing a wild goose but have the day off and got to thinking.... Any thoughts??

  2. #2
    Join Date
    Sep 2005
    Location
    Capital Area, New York
    Posts
    49
    I would like to know also.
    Tony Stone

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,910
    Moved to tech to Tech forum.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Apr 2012
    Location
    Texas
    Posts
    196
    You would have to contact the design engineers.

    "Different manufacturers have various methods for determining target subcooling. For superheat, most manufacturers use the same charts, but this is not true of subcooling. There is no substitute for having the manufacturer’s subcooling chart."

    Source:
    http://www.fieldpiece.com/tech-artic...-asx24-ash3#11

  5. #5
    Join Date
    Dec 2006
    Location
    Goodyear, AZ
    Posts
    197
    You can download this book it has a superheat chart, its FREE

    http://shop.rdholder.com/Troubleshoo...leshooting.htm

    FREE articles on Superheat, Subcooling and A/C Troubleshooting. For the FREE downloading of the articles go to Book and Papers on HVAC on the main page, put them in to the cart then, you must click on the PRINT AND CALL button for payment at check out. This method allows me to process your downloading at NO CHARGE.

  6. #6
    Join Date
    Apr 2009
    Location
    Pan Handle, Fl
    Posts
    599
    If it's not posted on name plate I have always used 10 as you stated.
    Insanity: Doing the same thing over and over again expecting a different outcome!

  7. #7
    Join Date
    Apr 2012
    Location
    Pasadena,Maryland
    Posts
    265
    The goodman units that I've installed all required 7 sc,carrier has it written on their data plates,but from what I've seen if you can't get the info,10-14 seer,10 is a good rule of thumb,some higher 15 seer units ask for 15 sc

  8. #8
    Join Date
    Sep 2008
    Location
    North carolina
    Posts
    42
    correct me if i am wrong but the 10* has to be read at the evaporator not the condenser for a true reading. if you have a long lineset that number may be alot higher at the condenser.

  9. #9
    Join Date
    Sep 2005
    Location
    Capital Area, New York
    Posts
    49
    Quote Originally Posted by tlp7 View Post
    correct me if i am wrong but the 10* has to be read at the evaporator not the condenser for a true reading. if you have a long lineset that number may be alot higher at the condenser.
    Yes I believe it is cracked you need to check the super sweet how cute is that a liter oil...

    Ok i will have to type this out. Voice recognition sucks on my tablet. Yes i believe you need to technically read super heat where it exits the evaporator coil.

    Tony Stone
    Please excuse my brevity, sent from a piss poor quality mobile "operating system", aka "Android". TapaTalk application is okay I guess...
    Tony Stone

  10. #10
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    A forum member directed me to a phone app called hvac buddy. It has a target subcooling formula built in but I've yet to try it. If you look in the right location you can avoid paying the 10 bucks for it

    Sent from my HTC Sensation 4G using Tapatalk 2

  11. #11
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by hvac wiz 79 View Post
    A forum member directed me to a phone app called hvac buddy. It has a target subcooling formula built in but I've yet to try it. If you look in the right location you can avoid paying the 10 bucks for it
    I'm not sure how much I'd rely on that for anything, it certainly isn't intended for TXV equipped systems.
    If more government is the answer, then it's a really stupid question.

  12. #12
    Join Date
    Feb 2006
    Location
    USA
    Posts
    4,381
    Quote Originally Posted by mark beiser View Post
    I'm not sure how much I'd rely on that for anything, it certainly isn't intended for TXV equipped systems.
    Can't argue with you there & I'm not recommending it, just sharing what was shared with me. one thing i want an answer on is why the difference is so great depending the manufacturer

    Sent from my HTC Sensation 4G using Tapatalk 2

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by hvac wiz 79 View Post
    one thing i want an answer on is why the difference is so great depending the manufacturer
    There are a lot of games being played to maximize ARI efficiency numbers.

    By running the subcooling and superheat at lower levels, it reduces the condensing pressure, and increases the evaporator pressure, thus lowering the overall compression ratio.

    Having 3-5 of subcooling is fine if you only have the 10-15' lineset they use for generating the ARI numbers.
    If you have longer lines, and/or any lift, you will have to charge to a higher subcooling value to prevent flash gas.
    Flash gas will eat away at the systems efficiency much more than a slightly higher compression ratio, from charging to a higher subcooling value, will.

    Virtually 100% of the systems I work on have linesets that are >30' long, and almost always have a minimum of 8' of lift. >50' lines, with 20' of lift, is very common.
    In the typical application I see, if I were to charge a Lennox or Goodmana TXV equipped system to factory specs, it would loose a lot of capacity to flash gas in the liquid line.
    I don't have a particular axe to grind with Lennox or Goodmana, they are just the only two I have personal experience with listing low subcooling values in their charging specs. In Lennox's case, the subcooling target changes based on the indoor unit/coil, which is a red flag indicating that they are tailoring refrigerant charges to hit ARI rating targets, rather than best operation of the refrigerant cycle in real applications.

    You must have enough subcooling to offset the pressure drop of the liquid line, plus a couple of degrees as a buffer, or the system will not work correctly.

    Physics trumps manufacturers gaming the ratings system.
    If more government is the answer, then it's a really stupid question.

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